"The logic of nature" has determined that many rheumatic diseases follow characteristic patterns in the biochemical contents of their synovial effusions, in their distribution of involved joints, and in their selective injury to either convex or concave joint members. For the most part, the physiology of these patterns has been little studied and is not at all understood. This project will employ new concepts and techniques to address each of these problems during the course of a 5-year period. Synovial effusions will be studied as disorders of microvascular physiology emphasizing new techniques to measure the effective synovial blood flow, the rate of lymph-lymphatic drainage, and the vascular permeability as indicated by the reflection coefficients of specific plasma proteins. These findings will be correlated with well-studied variables such as total protein, lactate, glucose, respiratory gas content and pH. Studies of articular distribution patterns will focus on normal physiologic contrasts between joints and between individuals in the "Starling forces" in synovium and synovial fluid and on possible inter-joint differences in blood flow, lymphatic drainage and hydraulic conductivity of the normal synovium. Studies of convex and concave joint members will employ new experimental methods to pursue the hypothesis that convex components are more flexible than their concave mates and that they are substantially strengthened by the hydraulic properties of their fluid contents.